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Carbon nanotubes (CNTs) are thought to have higher elastic modulus and strength than carbon fibers. The recent development of spinnable multi-walled carbon nanotubes (MWNTs) enables us to produce unidirectional MWNT reinforced polymer-based composites with a higher volume fraction of CNTs. The results of tensile tests of spinnable MWNTs in scanning electron microscopes show, however, that Young's modulus and tensile strength of MWNTs are not as high as expected. Annealing and developing thinner spinnable MWNTs will be the solution to improving the tensile property. In this study, as-produced and annealed untwisted yarns composed of MWNTs with three different diameters were prepared, and the tensile properties of spinnable MWNTs were estimated from the tensile properties of the untwisted yarns to investigate the effect of annealing and diameter on the overall tensile property of MWNTs. Furthermore, tensile tests of unidirectional MWNT reinforced epoxy composites were conducted and the contribution of the tensile property of MWNTs to the bulk tensile property of the composite was discussed. As a result, it was found that MWNTs with thinner diameters had higher Young's modulus and tensile strength and annealing improved Young's modulus of MWNTs, in addition to that the bulk tensile property of unidirectional MWNT reinforced epoxy composites was primarily determined by the tensile property of MWNTs. The results support previous findings from a limited number of tensile tests in SEM/TEM, and also reveal the validity of estimating the tensile properties of individual CNTs by tensile testing of untwisted yarns. In addition, the discussion on composite materials suggests that the tensile property of composite materials can be enhanced by improving the tensile property of MWNTs. [ABSTRACT FROM AUTHOR]

The effects of hot-water aging on the quasi-static and dynamic compression properties of unidirectional E-glass/epoxy laminates were investigated. E-glass/epoxy specimens were aged in water at 60°C for 4900 h and then aged and unaged specimens were tested in compression at a rate of 1.3·10–3 s–1 and by a split Hopkinson pressure bar apparatus at varying strain rates. Their diffusion behavior was successfully described by the two-stage model whose parameters were found by the nonlinear regression method. The strain-rate-sensitivity of aged and unaged E-glass-reinforced epoxy specimens in the longitudinal direction was studied. Their dynamic and static compression properties were compared for specimens with the same dimensions. Empirical models were proposed to predict dynamic properties as functions of strain rate. SEM micrographs showed a low degradation of the resin matrix and fiber-matrix interface at hot-water aging for a time up to 4900 h. [ABSTRACT FROM AUTHOR]

Replacing weaving and stitching used in textile-based reinforcements by using short fibers as a binder was discussed based on the tensile and compressive properties of [0], [± 45], and [0/90] laminates. A slight decrease in the longitudinal properties of the [0] composites was accompanied by a significant reduction of the properties of variability. In the case of [± 45] laminates, the presence of the short flax fiber shows a positive effect on the tensile, shear, and compressive properties. The mechanical properties of [0/90] laminates have shown a limited effect of the short fibers, with a slight decrease of both modulus and strength.

Carbon nanotubes (CNTs) are thought to have higher elastic modulus and strength than carbon fibers. The recent development of spinnable multi-walled carbon nanotubes (MWNTs) enables us to produce unidirectional MWNT reinforced polymer-based composites with a higher volume fraction of CNTs. The results of tensile tests of spinnable MWNTs in scanning electron microscopes show, however, that Young’s modulus and tensile strength of MWNTs are not as high as expected. Annealing and developing thinner spinnable MWNTs will be the solution to improving the tensile property. In this study, as-produced and annealed untwisted yarns composed of MWNTs with three different diameters were prepared, and the tensile properties of spinnable MWNTs were estimated from the tensile properties of the untwisted yarns to investigate the effect of annealing and diameter on the overall tensile property of MWNTs. Furthermore, tensile tests of unidirectional MWNT reinforced epoxy composites were conducted and the contribution of the tensile property of MWNTs to the bulk tensile property of the composite was discussed. As a result, it was found that MWNTs with thinner diameters had higher Young’s modulus and tensile strength and annealing improved Young’s modulus of MWNTs, in addition to that the bulk tensile property of unidirectional MWNT reinforced epoxy composites was primarily determined by the tensile property of MWNTs. The results support previous findings from a limited number of tensile tests in SEM/TEM, and also reveal the validity of estimating the tensile properties of individual CNTs by tensile testing of untwisted yarns. In addition, the discussion on composite materials suggests that the tensile property of composite materials can be enhanced by improving the tensile property of MWNTs.

Replacing weaving and stitching used in textile-based reinforcements by using short fibers as a binder was discussed based on the tensile and compressive properties of [0], [± 45], and [0/90] laminates. A slight decrease in the longitudinal properties of the [0] composites was accompanied by a significant reduction of the properties of variability. In the case of [± 45] laminates, the presence of the short flax fiber shows a positive effect on the tensile, shear, and compressive properties. The mechanical properties of [0/90] laminates have shown a limited effect of the short fibers, with a slight decrease of both modulus and strength. [ABSTRACT FROM AUTHOR]

Models for unidirectional fiber-reinforced hybrid composites of a regular periodic structure that allow one to determine the yield loci for fibrous composites are constructed. The plane stress state in all components of compositions having different tensile and compressive strengths is considered. Components of the compositions are homogeneous and isotropic, and their mechanical behavior is described by the associated flow rule for rigidplastic bodies with piecewise linear yield states of Johansen, Hu, and Tresca–Hu types. Analytical expressions for the equations of yield loci convenient for a further analysis and application are obtained. It is proved that the plastic flow in the reinforced medium is associated with the yield loci constructed. It is shown that, in contrast to the structural model with a one-dimensional stress state in fibers (Nemirovsky and Mruz–Shamiev models), considering the complex stress state in the reinforcement in the case of different yield stresses of composite components, in the general case, leads to yield loci with more than six regimes of plastic flow. [ABSTRACT FROM AUTHOR]

The present work reports a novel approach to enhance the fracture resistance and notch sensitivity of carbon fiber-reinforced polymer composites utilizing additive manufacturing (3-D printing) fabrication. The 3-D printed composites utilize carbon fiber bundles to reinforce nylon/chopped fiber resin in a multilayered structure configuration. Single-edge (60°) notched samples were printed using Mark Two printer. Three reinforcement schemes were designed and used to manufacture the specimens. The focus was placed on selective reinforcement at the crack tip to arrest crack initiation. The mechanical properties, fracture toughness, and fracture behavior of the printed composites were evaluated. It was found that wrapping fiber around the notch effectively blunted the notch and redirected crack propagation away from the notch tip, thereby lengthening the crack path and leading to improved fracture resistance. It was also found that such improvement reaches a saturation level. Excessive notch reinforcement beyond optimal limit can reverse the gains in fracture resistance due to notch-targeted reinforcement. Examination of the fracture surface morphology of the printed composites reveals lack of fusion of the sizing of the individual continuous carbon fiber bundles and the lack of adhesion between the matrix layers (nylon/chopped fiber resin) and the adjacent carbon fiber bundle reinforcement. Damage to the fibers within the carbon bundle was also observed. Thus, a synergetic effect of the carbon fiber bundles reinforcement and the matrix requires more optimization to manufacture carbon-reinforced polymer composites using 3-D printing. [ABSTRACT FROM AUTHOR]

Using the previously constructed equations of the theory of the plane multi-layer beams with a thin-layer structure in thickness, based on a discrete-structural model, a linear problem on the formation of the initial (subcritical) stress-strain state in test specimens of a unidirectional laminated composites with the [90°]s structure was given in shear tensile-compression tests. A numerical method was developed for solving the formulated problem, based on the reduction of the original problem to a system of integro-algebraic equations and the construction of their solution by the method of finite sums. The properties of the constructed equations are investigated and numerical experiments are carried out on the basis of the developed method. It is shown that in the test specimens of the laminated composite of the considered structure at their tension (compression) in the direction across the fibers and in shear, predominantly normal tensile (compression) stresses are formed, which are constant along the length and width of the specimen, and the tangential stresses in these directions are variable. [ABSTRACT FROM AUTHOR]

The paper presents a method making it possible to reveal the minimum cross-sectional area, maximum volume fraction of filaments (fibers) of a roving, and minimum volume fraction of the interfilament gaps of a dry roving, which are independent parameters (constants) of roving. Each kind of roving taken separately has parameters relevant only to it (technical data). Practical application of the method is demonstrated by examples of determination of these data for rovings of carbon (CF) and ultrahigh-molecular-weight polyethylene (UHMWPE). The ratio of the cross-sectional areas of the resin-impregnated and dry roving depends on the amount of matrix within the interfilament gaps and is a constant, which is assigned by the impregnation technology. The constants of rovings are a base for calculation of the reinforcement factors for components of composite. The constants make it possible to simplify the calculation of the number of rovings at prespecified concentration of reinforcement components in hybrid composites made of unidirectional fibers. Examples of utilization of the constants for the calculation of volume, required quantity, density, and volume fractions of reinforcement components in composites made of unidirectional fibers are presented. The difference of degree between actual volume fractions of fibers in the rovings and ideal values calculated for hexagonal and tetragonal spacing of fibers is revealed too. [ABSTRACT FROM AUTHOR]

Models of unidirectionally and orthogonally fiber-reinforced hybrid media of a regular periodic structure allowing one to determine the yield loci for these composites are constructed. Phase materials of the compositions are isotropic, and their mechanical behavior is described by the associated flow rule for rigid-plastic bodies with the Tresca yield condition. A plane stress state is assumed in the composition and all its components, and fibers are oriented along the directions of principal stresses in the composite body. The cases of rectangular and arbitrary cross sections of reinforcing fibers are considered. Analytical expressions for equations describing the regimes of yield conditions are obtained. Different passages to the limit of a homogeneous medium are investigated. Yield loci calculated by the models proposed and the widely used structural model with a one-dimensional stress state in fibers are compared. Yield loci in the case of imperfect adhesion between the reinforcement and binder material are constructed. [ABSTRACT FROM AUTHOR]

Natural fiber-reinforced composites are carbon-neutral materials that are anticipated for use as an alternative to glass fiber-reinforced plastics. This study investigated the effects of matrix ductility on the fatigue strength of unidirectional jute spun yarns impregnated with biodegradable plastics. Polylactic acid (PLA) and polybutylene succinate (PBS) were used for the matrix. PLA is brittle, but it is widely used as a matrix of green composites. Because PBS has much higher ductility than that of PLA, it can be expected to have higher fatigue strength when subjected to the same strain amplitude as PLA. Fatigue tests were conducted with maximum stress set to 40-90% of the tensile strength. The stress ratio was set as 0.1. Results show that the matrix ductility strongly affects the fatigue strength and the fatigue mechanism of the composite. A matrix with better ductility was effective to improve fatigue strength. [ABSTRACT FROM AUTHOR]

The current study reports on the visualization methodology applied for the units which represent the media of fibre-reinforced materials under conditions of large deformations. The units are visualized by the numerical solutions of the boundary problem, which shows the load on the materials in the deformed media. 3-D images of the deformed materials configurations are given with their unidirectional, bidirectional and three-directional schemes of reinforcement. These configurations are calculated with two level Akhundov's carcass theory employed for a piece of a homogeneous body. [ABSTRACT FROM AUTHOR]

Introduction: Most denture fractures occur within the mouth due to resin flexural fatigue. For example, the deep labial notch at the high labial frenum causes denture breakage, as can deep scratches and generated processing stresses. The rising cost of annual prosthetic repairs is evidence that the problem of total denture fracture has not been solved. The purpose of this investigation was to evaluate the relative improvement in flexural strength between heat-cured polymethyl methacrylate (PMMA) resin reinforced with glass fibers (GF) and basalt fibers (BF) of varied orientations., Material and Methods: A total of 150 heat-cured acrylic resin specimens of 65x10x3 mm dimension were prepared, 30 of which were left unreinforced (Group A), 30 of which were reinforced with GF in transverse pattern (Group B), 30 of which were reinforced with GF in meshwork pattern (Group C), 30 of which were reinforced with BF in transverse pattern (Group D), and 30 of which were reinforced with BF in meshwork pattern (Group E). All of the samples were put through flexural strength testing on the universal testing machine. One-way ANOVA and the Tukey-Kramer various correlation test (= 0.05) were used in SPSS for Windows to look at the facts., Results: The mean flexural strength for Group A was 46.26±2.26 MPa, 64.98±1.53 MPa for Group B, 76.45±2.67 MPa for Group C, 54.22±2.24 MPa for Group D, and 59.02±2.38 MPa for Group E. Flexural strength was impacted by both the kind of BF and GF reinforcement (F = 768.316, P = 0.001)., Conclusion: Within the limitation of the current research, BF reinforcement outperforms GF reinforcement and unreinforced heat-cured acrylic resin in terms of flexural strength., Competing Interests: The authors have declared that no competing interests exist., (Copyright © 2023, Nayak et al.)

A heuristic approach to determining the effective thermal conductivity coefficients of unidirectionally reinforced biperiodic composite media is suggested allowing one to substantially refine the calculated values of the effective coefficients of transverse thermal conductivity of the indicated compositions by using the simplest partitioning of a periodicity cell into thin layers (subelements) with subsequent application of the simplest formulas of averaging by simple and inverse mixture rules. A comparison of the calculated values of these coefficients with familiar experimental data is made. The good agreement of the prediction with experiment allows an assumption that the method developed can be used for practical calculations of the thermophysical characteristics of fibrous media with biperiodic structure. At the present time the accuracy of more complex structural models of the thermal conductivity of unidirectionally reinforced composites lacks a strict experimental justification. [ABSTRACT FROM AUTHOR]

On the basis of single-level applied and two-level carcass theories, large deformations of regularly fiber-reinforced bodies are examined. Results of solution of the problem on pressure-reduction of unidirectionally reinforced prismatic and cylindrical bodies rigidly fixed at their end faces, whose matrix and fibers are made of compressible materials, are presented. The results obtained by both the theories are compared, and the possibility of using, under the conditions considered, solely the carcass theory in investigating pressurt-reduced bodies highly filled with fibers is clarified. [ABSTRACT FROM AUTHOR]

Using a numerical experiment method, the authors have solved a problem of optimization for a three-layer metal-composite cylinder of finite length, which is loaded with axisymmetric internal explosion. The optimization consists in finding the best layer thickness ratio and reinforcement configuration for the cylinder's anisotropic composite part in order to provide the maximum strength margin by Tsai-Wu criterion for the fixed overall dimensions of the cylinder and the relative explosive charge mass. The use of an elastoplastic isotropic steel 20 for the internal layer is demonstrated to significantly improve the metal-composite cylinder strength owing, in particular, to plastic yielding, in comparison to a purely composite cylinder. The use of high-strength steels with a high yield stress is not advisable. The application of all-metal shells is impractical from the standpoint of materials consumption - they are too heavy. [ABSTRACT FROM AUTHOR]

Calculation and experimental study of transverse tension and compression of a rubber-cord composite with a unidirectional scheme of reinforcement is presented. The calculation results for components of the composite and for the composite as a whole are compared with the experimental data. The loss of stability of the deformed rubber-cord composite in transverse tension is analyzed. [ABSTRACT FROM AUTHOR]

Determination of the interlaminar properties of laminate composites to date have included a few direct measurement techniques: the standardized short beam test via three-point flexural testing and the double beam shear test via five-point flexural testing. These test methods are limited to a determination of the apparent interlaminar strength, while the full stress-strain behavior cannot be determined. The double beam shear test allows for a calculation of the shear modulus, provided that four additional elastic, in-plane properties have been determined in advance via three additional types of tests. The present work includes a comparison of the three-point short beam test, the non-standardized four-point flexural test and the double beam shear test (requiring small span-length-to-thickness ratios for the shear loading to become dominant). The tests are carried out on unidirectional carbon fiber reinforced composite (CFRP-UD) with a symmetric layup. The experiments are accompanied by photomechanical investigations using digital image correlation (DIC) to visualize the phenomenology of shear deformation. The novelty of this approach includes the use of the DIC determined shear strains, which show a parabolic distribution across the specimen's thickness. The DIC calculated maximum shear strain across the thickness is used for a full description of the stress-strain behavior with a focus on the elastic loading range to evaluate the shear modulus. Interlaminar shear strengths and shear moduli determined from all three types of tests are compared to the intralaminar shear properties.